Update: (O.S.C.A.) question now resolved - applied to all 1500 S Cabriolet [118S] and 1600 S Cabriolet [118SA] and [118SB] because it was an OSCA engine design by the Alfieri brothers after they left Maserati. 1200 [118G] and 1500-without-S [118H] and [118K] used Fiat engines.